1
Q
What is the cytoskeleton?
A
A network of three filament types that supports the cell and plays a key role in cell movement
2
Q
what are the three main cytoskeletal elements?
A
Microtubules (MTs), Microfilaments (MFs), and intermediate filaments (IFs)
3
Q
Describe microtubules (MTs)
A
Hollow, rigid cylindrical tubes made of tubulin subunits
4
Q
describe microfilaments (MFs)
A
solid, thin filaments made of actin
5
Q
Describe intermediate filaments (IFs)
A
tough, ropelike fibers composed of various related proteins
6
Q
What is a key property of cytoskeletal elements that allows them to function?
A
they are highly dynamic and can undergo rapid, dramatic reorganization
7
Q
What do cytoskeletal elements often require for their functions?
A
accessory proteins that are not part of the filaments
8
Q
What are two major functions of the cytoskeleton?
A
providing structural support and mediating cell movements
9
Q
what are microtubules?
A
Hollow, tubular structures found in most eukaryotic cells, including the mitotic spindle and the core of cilia and flagella
10
Q
What are the dimensions of a microtubule?
A
outer diameter-24nm; wall thickness -5nm
11
Q
how long can microtubules extend?
A
they may span the entire length or breadth of a cell
12
Q
what are microtubules made of?
A
polymerized aB-tubulin heterodimers
13
Q
What are MT-associated proteins (MAPs)?
A
Proteins that bind to microtubules; many are found primarily in brain tissue
14
Q
How is MAP binding regualted?
A
by adding or removing phosphate groups from specific amino acids
15
Q
What disease involves abnormal MAP phosphorylation?
A
Alzheimer’s disease
16
Q
What are two major structural functions of microtubules?
A
Providing structural support and acting as cellular organizers
17
Q
What is intracellular motility?
A
Directed movement of macromolecules and organelles within the cell
18
Q
What are two examples of intracellular motility involving MTs?
A
Axonal transport and organelle transport
19
Q
What are the two MT motor proteins?
A
Kinesin and dynein
20
Q
Which direction does kinesin move cargo?
A
Anterograde (usually toward the cell periphery); requires ATP
21
Q
What direction does dynein move cargo?
A
Retrograde, opposite to kinesin
22
Q
What compound specifically inhibits microtubules?
A
Colchicine, a plant-derived chemical that causes rapid MT depolymerization
23
Q
why are they called intermediate filaments?
A
because their diameter (-10nm) is between that of microfilaments (MFs) and microtubules (MTs)
24
Q
what is the diameter of intermediate filaments?
A
approximately 10nm
25
what do intermediate filaments look like under electron microscopy (EM)?
solid, smooth-surfaced, unbranched filaments
26
in what types of cells are intermediates found?
they are identified with certainty only in animal cells
27
how are intermediate filaments arranged within the cell?
They radiate throughout the cytoplasm of many animal cells
28
How are IFs connected to other cytoskeletal elements?
by thin, wispy cross-bridges that link them to microtubules and microfilaments
29
what are microfilaments (MFs)?
Solid, thin cytoskeletal fibers
30
What is the diameter of microfilaments?
about 8nm
31
What are microfilaments made of?
Globular actin (G-actin) subunits that polymerize into filamentous actin (F-actin)
32
What motor protein moves along microfilaments?
Myosin
33
What is the relationship between actin and myosin?
Myosin uses ATP to move along actin filaments, enabling cell movement, muscle contraction, and vesicle transport
34
What is unusual about skeletal muscle cell structure?
They are long, cylindrical cells (10-100 micrometers thick; up to >100 mm long) and contain hundreds of nuclei
35
Why are skeletal muscle cells multinucleate?
Because they form by the embryonic fusion of many mononucleate myoblasts.
36
What is another name for skeletal muscle cells?
Muscle fibers, due to their elongated fiber-like shape
37
What is a muscle fiber composed of?
hundreds of thinner cylindrical strands called myofibrils
38
what is a sacromere?
the basic contractile unit of muscle, arranged end-to-end along myofibrils
39
What are the major structural components of a sacromere?
Z-line, I-band, A-band, and H-zone
40
During muscle contraction, what happens to the sacromere?
The sacromere shortens as thin filaments slide past thick filaments
41
What proteins make up the thin filaments?
Actin, tropomysoin, and the troponin complex
42
What is the role of tropomyosin?
It covers the myosin-binding sites on actin when the muscle is relaxed.
43
what is the role of troponin?
Troponin binds Ca2+, causing tropomyosin to shift and uncover myosin-binding sites on actin.
44
Why does Ca2+ cause muscle contraction?
Ca2+ binds to troponin-> tropomyosin moves -> myosin-binding sites exposed -> cross-bridges form -> contraction
45
Why does a drop in Ca2+ cause muscle relaxation?
Tropinin releases Ca2+ -> tropomyosin covers binding sites again -> myosin cannot attach -> muscle relaxes
46
What is meant by the "functional anatomy" of a muscle fiber?
It includes myofibrils, sacromeres, the sacrolemma, T-tubules, sarcoplasmic reticulum (SR), and mitochondria-structures required for contraction
47
What is the 3rd tenet of Cell Thoery?
New cells originate only from other living cells, through cell division
48
What are the two major phases of the cell cycle?
M phase and Interphase
49
What happens during M phase?
Mitosis- separation of duplicated chromosomes into two nuclei
cytokinesis-division of the cell and cytoplasm
50
What is interphase?
The phase that occupies the majority of the cell cycle, when the cell grows and duplicates its DNA
51
What are the three subphases of interphase?
G1 (first gap), S (DNA synthesis), and G2 (second gap)
52
What occurs during G1 phase?
The cell grows and carries out normal functions; prepares for DNA replication
53
What occurs during S phase?
DNA is replicated
54
What occurs during G2 phase?
cell prepares for mitosis by making proteins and checking DNA
55
What is G0 phase?
a specialized resting state where cells are not actively preparing to divide
56
what kinds of cells are usually in G0?
Most fully differentiated cells in the body (neurons, muscle cells)
57
What do cell checkpoints do?
ensure the cell only proceeds if conditions are correct and DNA is undamaged
57
What are the two major cell cycle checkpoints?
G1->S and G2->M
58
What is MPF?
Maturation-promoting factor, a protein complex that triggers entry into M phase
59
What type of enzyme is MPF?
a 2-subunit protein kinase
60
What are the two subunits of MPF?
1. catalytic subunit (the kinase)
2. regulatory subunit: cyclin
61
Why is the regulatory subunit called "cyclin"?
Because its concentration rises and falls cyclically during the cell cycle
62
When is MPF active?
Only when the cyclin levels reach a critical threshold, allowing the catalytic subunit to function
63
what happens when MPF is activated?
the cell enters M phase (mitosis)
64
What ultimately determines MPF activity?
cyclin concentration
65
what is mitosis?
a process of nuclear division in which replicated chromosomes are equally segregated into two nuclei
66
where does the name "mitosis" come from?
from greek mitos, meaning thread, referring to the threadlike appearance of chromosomes
67
what is the main purpose of mitosis?
to ensure accurate segregation of duplicated DNA into two daughter nuclei
68
What are the stages of mitosis?
prophase, prometaphase, metaphase, anaphase, telophase
69
what happens during prophase?
chromosomes condense, and the mitotic spindle begins to form
70
what happens during prometaphase?
the nuclear envelope breaks down; spindle fibers attach to kinetochores
71
what happens during metaphase?
Chromosomes align at metaphase plate
72
what happens during telophase?
Chromosomes decondense and nuclear envelopes re-form around the two sets of DNA
73
what happens during anaphase?
sister chromatids separate and move toward opposite spindle poles
74
What is cytokinesis?
The physical division of the cell into two separate daughter cells by partitioning the cytoplasm
75
Are the daughter cells genetically identical after mitosis and cytokinesis?
yes, they are genetically identical to each other and to the original mother cell
76
What is meiosis?
A process in which chromosomes number is reduced, producing haploid cells from diploid cells
77
How does meiosis achieve chromosome reduction?
through two sequential cell divisions (meiosis I and meiosis II) after one round of DNA replication
78
What are the two major stages of meiosis?
meiosis I and meiosis II
79
what is the key event of meiosis I?
separation of homologous chromosomes
80
what is the key event of meiosis II?
separation of sister chromatids, similar to mitosis
81
what is one major similarity between mitosis and meiosis?
both involve stages like prophase, metaphase, anaphase, and telophase
82
What is one major difference between mitosis and meiosis?
mitosis produces 2 identical diploid cells, while meiosis produces 4 genetically divers haploid cells
83
what is synapsis?
pairing of homologous chromosomes during prophase I of meiosis
84
What is synaptonemal complex (SC)?
a protein structure that forms between synapsed homologues during synapsis
85
what is bivalent?
a pair of homologous chromosomes that have synapsed
86
what is a tetead?
a bivalent containing four chromatids (two from each homologue)
87
What are chiasmata?
Point(s) where homologous chromosomes remain attached after crossing-over
88
what is crossing-over?
the physical exchange of DNA between nonsister chromatids of homologous chromosomes
89
what is the result of crossing over?
genetic recombination that produces new allele combinations, increasing genetic diversity
90
what structure forms during recombination due to reciprocal DNA exchange?
a heteroduplex joint molecule with Holliday junctions
91
What is a Holliday junction?
a cross-shaped DNA structure representing the crossover point between homologous chromatids
92
what is the biological purpose of meiosis?
to produce haploid gametes and increase genetic variation
93
what controls cell number?
The balance between cell division and cell death (apoptosis)
94
what controls cell size?
regulation of cell growth and progression through the cell cycle
95
How are cells organized in multicellular organisms?
into tissues
96
what is the extracellular matrix (ECM)?
an organized network of materials outside the cell membrane
97
What is one major role of the ECM?
It regulates cell shape and cell activities
98
Does the ECM look the same in all tissues?
no- its structure varies, but it contains similar core components across tissues
99
in which tissues is ECM especially prominent?
Connective tissues (cartilage, bone, tendons, cornea)
100
What are the major components of the ECM?
collagens, proteoglycans, fibronectin, laminin, and other ECM proteins
101
what is collagen?
a major structural protein of the ECM
102
What is the main function of collagen fibers?
to provide strength, rigidity, and elasticity to tissues
103
where is collagen found?
Only in the ECM
104
What are proteoglycans?
protein-polysaccharide complexes found in the ECM
105
What is the main function of proteoglycans?
they trap water and form the gel-like ground substance of tissues
106
what roles do fibronectin and laminin play ini the ECM?
They help connect cells to the ECM and organize the matrix
107
Why is the ECM important overall?
it supports cells structurally, regulates their behavior, and helps organize tissues
108
What are integrins?
integral membrane proteins that connect cells to the extracellular matrix (ECM)
109
what is the structure of an integrin?
a heterodimer made of two subunits: alpha and beta
110
where are integrins found?
on surface of most vertebrate (animal) cells
111
are integrins always active?
no- many integrins are on the cell surface in an inactive conformation and can be activated by internal signals
112
what peptide sequence do many integrin-binding ECM proteins contain?
the RGD sequence: arginine-glycin-aspartic acid
113
what are embryonic stem cells?
stem cells early embryos that are pluripotent (can form nearly any cell type)
114
what are induced pluripotent stem cells (iPSCs)?
Adult cells reprogrammed back to a pluripotent, stem-cell-like state
115
what is cancer?
uncontrolled cell proliferation forming malignant tumors that invade healthy tissue
116
why does cancer have a genetic basis?
Because it results from mutations in specific genes, though it is usually not inherited
117
what is "contact inhibition" and how do cancer cells behave?
normal cells stop dividing when crowded; cancer cells lose contact inhibition and grow over each other
118
Are cancer cells immortal or limited in cell divisions?
immortal-they divide indefinitely
119
What is one reason cancer cells proliferate more easily?
they are less dependent on growth factors than normal cells
120
What happens to chromosomes in cancer cells?
they show instability and abnormalities
121
why are cancer cells called clonal?
because all cells in a tumor originate from one original mutated cell
122
What are the main causes of cancer?
carcinogenic chemicals, radiation (like UV), certain viruses, and environmental factors
123
how do carcinogens like chemicals or UV light contribute to cancer?
they cause mutations in DNA
124
How can viruses contribute to cancer?
some viruses can infect cells and transform them into cancer cells (HPV is strongly linked to cervical cancer)
125
Is cancer usually caused by a single genetic change?
no, cancer typically requires multiple genetic alterations
126
What does it mean that cancers are "monoclonal"?
a tumor usually originates from a single strand mutated cell that proliferates uncontrollably
127
What are the two major gene categories involved in cancer?
tumor-supressor genes and oncogenes
128
what do tumor-supressor genes do?
they act as cell-growth brakes, preventing uncontrolled proliferation (they are recessive-both copies must be lost)
129
what do oncogenes do?
they act as accelerators, pushing cells toward uncontrolled growth when activated (they are dominant- one altered copy is enough)
130
why is cancer relatively rare given constant DNA damage?
because developing malignancy requires multiple mutations, not just one
CB Midterm
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